1. Field of the Invention
The present invention relates generally to surgical implants and, more particularly, relates to alloplastic spinal disk implants and procedures.
2. Description of the Related Art
Spinal disks comprise a central region called the nucleus pulposus surrounded by a second region known as the annulus fibrosis. The annulus fibrosis portion comprises collagen fibers that may weaken, rupture, or tear, leading to compromised annular confinement of the nucleus and producing disk bulges, herniations and other disk pathologies.
The major causes of persistent, often disabling, back pain are disruption of the spinal disk annulus fibrosis, chronic inflammation of the spinal disk (e.g., herniation), or relative instability of the vertebral bodies surrounding a given spinal disk, such as the instability that often occurs due to a degenerative disease. Spinal disks mainly function to cushion and tether the vertebrae, providing flexibility and stability to the patient's spine. Functionally speaking, spinal disks comprise a central hydrostatic cushion, the nucleus pulposus, surrounded by a containing multi-layered ligament, the annulus fibrosis. As spinal disks degenerate, they can, for example, lose their water content and height which brings the vertebrae closer together. This phenomena results in a weakening of the shock absorption properties of the spinal disk and a narrowing of the nerve openings in the sides of the spine which may pinch the nerve.
This spinal disk degeneration can eventually cause back and leg pain. Weakness in the annulus fibrosis from degenerative spinal disks, or from spinal disk injury, can allow fragments of nucleus pulposus within the spinal disk space to migrate into the spinal canal. There, displaced nucleus pulposus or protrusion of annulus fibrosis, e.g., herniation, may impinge on spinal nerves. The mere proximity of the nucleus pulposus or a damaged annulus fibrosis to a nerve can cause direct pressure against the nerve, resulting in numbness and weakness of leg muscles.
It is estimated that approximately 80% of the population at some time in their life suffer back injuries necessitating consultation from a medical doctor for treatment of back pain. A good portion of these back injuries are related to spinal disk protrusions or herniations, and a smaller percentage are related to internal disk derangement.
Often, inflammation from spinal disk protrusions or herniations can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. In some cases, the spinal disk tissue is irreparably damaged, thereby necessitating removal of a portion of the spinal disk or the entire spinal disk to eliminate the source of inflammation and pressure. At the present time, a procedure which is performed as an open procedure is called a microdiskectomy in which small midline incision is made in the lumbar spine with the dissection being carried down to the lamina. The lamina is then prepared with a keyhole laminotomy, and the ligamentum flavum is then removed. Once this occurs the cal sac and nerve root are retracted to the contralateral side, thus providing exposure to the disk space. Intraoperative lateral x-ray can be implemented to confirm the position of the disk, and direct visualization of the herniation can be noted. Typically, a 15-blade is used to make an annulotomy, and the removal of the herniated fragment or fragments is then undertaken. In some cases this completes the disk excision procedure, while in other cases the surgeon actually places a pituitary rongeur or ring curette into the disk space and removes additional disk material, but a subtotal diskectomy is performed. At the conclusion of the surgery, the offending disk fragment or fragments has been removed, and there is now an annular defect that varies in size. This defect may be as small as 0.5 mm×0.5 mm and as large as 10 mm×15 mm. Typical annulotomies, however, are approximately 5 mm×5 mm. Many current technologies fail to offer surgeons plugs or other materials to place into the disk space for preventing recurrent disk herniation.
To overcome the disadvantages of traditional traumatic spine surgery, minimally invasive spine surgery was developed. Endoscopic spinal procedures, for example, are less invasive than open spinal procedures. In an endoscopic procedure, the spinal canal may not be violated and therefore epidural bleeding with ensuring scarring may be minimized or avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open diskectomy. Further, more rapid rehabilitation facilitates faster recovery and return to work. Minimally invasive techniques for the treatment of spinal diseases or disorders include diskography, chemonucleolysis, laser techniques and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disk(s) for passage of surgical instruments, implants and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the procedure (e.g., laparoscopic, thoracoscopic, arthroscopic, back, etc.). Once the operating corridor is established, the nerve root may be retracted and a portion or all of the spinal disk removed. Following removal, typical techniques do not implement an annular sealant or other means to efficiently and effectively treat the annular defect or opening to minimize the possibility of recurrent complications such as, for example, future nuclear herniations.